Studies are proposed in which the control of steroid hormone receptor activity will be investigated as a function of alterations in a discrete series of endogenous and exogenous factors and conditions, in experiments where the general receptor milieu is maintained as constant as possible. Hormonal induction of changes in the intracellular dynamics of estrogen receptor turnover will be studied by quantifying the roles of receptor synthesis, reutilization and recycling in the process of cytosol receptor replenishment; intracellular compartmentalization of receptors will constitute an integral part of this analysis. The function of pyridoxal-5'-posphate as a modulator of estrogen receptor activity will be explored in relation to its ability to alter nuclear activity of uterine receptors and to induce structural changes in the receptor system will be addressed in the same manner, with additional analysis of its modification by prolactin. The mechanism of action of 4-mercuri-17 beta-estradiol as an estrogen will be further characterized with respect to its function in cytoplasmic and post-transcriptional nuclear reactions. The effects of LHRH on anterior pituitary estrogen receptor activity will be explored, as well as the relationship between depletion-replenishment and gonado-tropin secretion in this tissue; both castrate and neonatally-androgenized rats will be the models of choice in these studies.